湿热环境中碱性泥浆附着下镀锌钢板的腐蚀行为

通过在湿热环境中进行高温高湿条件下进行腐蚀实验,研究了在泥浆附着条件下汽车用热浸镀锌钢板的腐蚀行为,观察了腐蚀的发展过程,并利用SEM和XRD等手段对腐蚀产物进行了观察和分析.结果表明,镀锌板的泥浆腐蚀过程可分为形成白锈的镀锌层腐蚀以及形成红锈和黑锈的基体腐蚀2个阶段.基体腐蚀产物中γ-FeOOH含量较高,而且泥浆中Cl-的富集对腐蚀产物的保护性具有加速破坏作用.在较低温度时,腐蚀失重率逐渐降低;而在较高的温度下,腐蚀失重率则出现先降后增的转折点,主要原因是温度升高导致腐蚀界面反应加速.在腐蚀过程中,腐蚀电位会发生从低至高的跃迁,分别对应着镀锌层和钢基体的腐蚀过程.环境温度提高,将导致电位跃迁提前.

CORROSION BEHAVIOR OF THE HOT-DIP GALVANIZED STEEL SHEET UNDER ADHESION OF AN ALKALINE MUD IN HOT-HUMID ENVIRONMENTS

The corroded behavior of the hot--dip galvanized (HDG) steel sheet used in automobile under mud adhesion was investigated by the hot and humid corrosion test. The corrosion products were observed and analyzed by means of SEM and XRD. The results show that the corrosion process of the HDG steel sheet with the mud adhesion could be divided into two steps, i.e., the formation of white rust due to corrosion of the zinc coating and the formation of red--black rust due to corrosion of the steel substrate. The content of γ--FeOOH in the corrosion products of the substrate is higher than others and the aggregation of Cl^- ions in the mud accelerates the failure of the protection of the rust layer. The corrosion mass--loss increases continually with time but the corrosion mass--loss rate decreases correspondingly. The corrosion mass--loss rate at the higher temperature increases suddenly after a period of exposing time because the high temperature accelerates the interface reactions. In the corrosion process, there is a jump in the corrosion potential from a lower to a higher value, corresponding to the corrosion process of the zinc coating and the steel substrate, respectively. The potential jump will become earlier with temperature increasing.